The present invention relates to an optical detector assembly, and more particularly to an optical dust detector assembly adapted for use in an automotive vehicle for detecting the concentration of dust, smoke or the like contained in a flow of air passing therethrough.
An optical dust detector assembly of this type includes a cylindrical air duct member having an introductory portion with an inlet opening, and a base portion with an outlet opening, for permitting dust-containing air to pass therethrough, the air duct member having a pair of radial holes formed in its peripheral wall and opposed to each other, a pair of cylindrical casings secured to the peripheral wall of the air duct member on both lateral sides thereof with respective opening ends communicating with the interior of the air duct member through the respective radial holes thereof, a light emission element arranged within one of the casings to emit a light beam therefrom and pass it through the radial holes toward the other casing, and a light receiving element arranged within the other casing to receive the light beam emitted from the light emission element and passed through the radial holes, the light receiving element detecting a decrease in the intensity of the received light beam caused in response to an increase of the dust concentration in the air introduced into the air duct member through the introductory portion thereof.
In such a conventional optical dust detector assembly as described above, depending on the position of the detector assembly in the vehicle, small foreign particles such as dirt, rain, snow, sleet or water splash may be present in the dust-containing air introduced through the introductory portion of the air duct member. This causes the intensity of the received light beam to be varied due to the presence of those foreign particles other than dust. In other words, the optical dust detector assembly will detect not only dust to be detected but also those foreign particles other than the dust, resulting in the occurrence of errors in dust detection. Furthermore, by adhesion of the foreign particles to the light emission element, light receiving element or other optical elements, the optical functions of the dust detector assembly may deteriorate.